Over the past several years, IC technology has been applied to the production of various sensing devices and to the integration of sensors and circuits. Among the many advantages of this approach are precision and designability, extreme miniaturization, integration with signal-detection and conditioning circuits, and low cost, as a result of batch processing.
The most widely applied microprocessed silicon sensors have been diaphragm pressure transducers, particularly for applications at near atmospheric pressures.
Previous diaphragm sensors with piezoelectric readouts have used diaphragms made of single-crystal silicon. Control of the thickness and of the latent stress in such diaphragms was inadequate for use at very thin dimensions. The best result reported, of which we know, is in Sensors and Actuators 4 (1983) 357-362, an article by Royer et al., which employed a diaphragm of elemental silicon 30 .mu.m thick and a ZnO piezoelectric film 3-5 .mu.m thick. The diaphragm then was 3 mm in diameter and the readout piezoelectric film consisted of an outer and an inner electrode concentric to each other and positioned on both sides of the ZnO film. The reported sensitivity was 25 .mu.V per .mu.bar a signal-to-noise ratio of 5:1 at 2 .mu.bar, a frequency response of 0.1 Hz to 10 kHz with a 10.sup.10 .OMEGA. shunt resistor, and a power consumption below 40 microwatts.